The oculomotor system of decapod crustaceans is useful as a model system to examine the nervous control of behavior, since it exhibits the property of memory, and because some of the reflexes involved in the control of eye movements appear to be ballistically executed, requiring a precision not encountered in most other reflex actions. In addition, modification of the crayfish visual system has occurred on several different occasions following the invasion of cave environments by primitive epigean generic stocks. These animals provide an opportunity to examine the effects of evolutionary selective pressures upon the structure and function of the oculomotor system - a nervous organization having a much reduced function in animals which are functionally blind. This research project hopes to examine the nature of these evolutionary changes and to provide some general predictions concerning the relative evolutionary stabilities of a number of the features in nervous functional organization.